1. Field of the Invention
The invention relates to a sealed battery. More particularly, the invention relates to a sealed battery in which a lid body and a battery container are joined by a double-rolled seam method, and to a vehicle equipped with the sealed battery.
2. Description of the Related Art
Lithium-ion batteries, nickel hydride batteries and other secondary batteries are gaining importance as vehicle-mounted electric power sources, or electric power sources of personal computers and portable terminals. In particular, the lithium-ion battery, which is light in weight and is able to obtain high energy density, is highly expected to be used as a vehicle-mounted high-output power source. In one example of the lithium-ion battery, an electrode body, an electrolyte solution and the like are contained in a metal-made battery container, and then a metal-made lid body is attached to an opening portion of the battery container, and is sealed thereto by joining their meeting portions by welding means such as laser welding or the like. However, the welding junction, such as the laser welding or the like, has an advantage of allowing the easy sealing with high airtightness, but is slow in the sealing speed and low in productivity. Besides, there is a need to provide means for preventing weld spatters (typically, metal dusts) that are produced at the time of laser welding from scattering into the inside of the battery. Therefore, it is required to build a sealing structure of a battery that achieves good productivity and high reliability. One sealing method for solving the foregoing problem is a method in which the lid body is joined to the battery container by using a so-called double-rolled seam method. In the double-rolled seam method, a curl of the lid body (a folded outer peripheral portion thereof), and a flange (a folded peripheral edge portion) formed on an opening end of the battery container are superposed on each other, and are rolled in together, and are bonded together by pressurizing the rolled portion from outside. If the double-rolled seam method is adopted, the junction of the lid body to the battery container can be carried out at high speed by a bending process, and there is no production of weld spatters or the like, and the prevention of entrance of foreign matter into the battery can easily be realized. Examples of the related art of this kind include Japanese Patent Application Publication No. 2000-149884 (JP-A-2000-149884).
In the foregoing kind of lithium-ion battery, it is desirable that high airtightness be maintained at the junction portion that is formed by the double-rolled seam method, even in a long-time use. That is, in the case where the battery is used under sever conditions for a long time (e.g., in a vehicle-mounted application), a gap between the lid body and the battery container tends to form in the double-rolled seam site (junction portion), and therefore there is a possibility of decline in the airtightness of the battery. In particular, in a lithium-ion battery with an insulation layer (e.g., a resin coat) formed on the lid body surface, since the insulation layer on the lid body surface and the metal forming the battery container, that is, different kinds of materials, are joined, a gap therebetween tends to form if the battery is used for a long time under severe conditions (e.g., in a place where severe vibrations can occur or where changes in temperature are severe, for example, inside a vehicle or the like).